Humidity sensors are widely used in various fields to measure the amount of water vapor present in the air of a particular environment. Humidity sensors are often configured as capacitive sensor devices that use capacitance to measure humidity. Capacitive humidity sensors typically include a pair of electrodes separated by a dielectric material. The dielectric layer is formed of a material, such as polymer that is configured to absorb and retain water molecules at concentrations that are proportional to the ambient humidity. The water molecules alter the dielectric constant of the polymer resulting in a change in capacitance between the two electrodes. Humidity can therefore be determined by measuring the capacitance between the two electrodes and correlating the measured capacitance to a corresponding humidity value.
Previously known capacitive humidity sensors often utilize flat, thin interdigital electrodes provided on a surface of a substrate and covered by a polyimide film for capacitance measurement. While such sensors are effective for measuring humidity, they can have a rather large footprint on the surface of the substrate which limits the ability to incorporate humidity sensors into other devices without increasing the size of the device. In addition, such sensors are generally not capable of being efficiently integrated into CMOS processing. As a result, separate chips and separate processing steps are typically required to fabricate capacitive humidity sensors, and special packaging methods are required to incorporate them into other devices.